Fluorescent lighting control circuit

Abstract

A control circuit for fluorescent lamps having gas filled tubes and a pair of discharge electrodes in the tubes includes a transformer, a gated switching device and a control signal generating circuit. The transformer has a secondary winding connected with the lamp discharge electrodes and a primary winding to which power is applied by the switching device when a gating signal is applied to its gating terminal. The control signal generating circuit normally controls the gating of the switching device by alternatingly applying, and then ceasing to apply, a control signal to the gating terminal. The control circuit is capable of continuing a current between the discharge electrodes once the lamp is conducting. The control circuit is further capable of "starting" a lamp by applying a high voltage to the discharge electrodes. The high voltage is generated when the gated switching device is not applying power to the primary winding. In order to avoid arcing and corona discharge in the control circuit as a result of misconnected and leaky fluorescent lamps, a voltage responsive device is connected with the gating terminal and responds to the voltage across the primary winding by applying a signal to the gating terminal in order to switch the switching device to apply power to the primary winding and, in this manner, causing the transformer to cease the generation of the damaging high voltage.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A control circuit for a gas discharge lamp, said lamp having a gas filled chamber and at least one pair of discharge electrodes in said gas filled chamber, said control circuit comprising: a transformer including a primary winding and a secondary winding;   a gated switch means having a gating terminal and selective conducting means responsive to a signal being applied to said gating terminal for applying a supply voltage to said primary winding;   control signal generating means for selectively applying a signal to said gating terminal when said control circuit is in a first state and for not applying a signal to said gating terminal when said control circuit is in a second state;   said secondary winding being adapted to attempting to establish a current between said discharge electrodes upon the occurrence of both a current not being conducted between said discharge electrodes and said control circuit being in said second state; and   protection means for applying a signal to said gating terminal upon the occurrence of both said control circuit being in said second state and failure of said secondary winding to establish a current between said discharge electrodes;   said secondary winding includes means for producing a high voltage in order to attempt to establish a current between said discharge electrodes and wherein said protection means includes means responsive to said high voltage exceeding a predetermined level.   
     
     
       2. The control circuit in claim 1 wherein said responsive means includes a voltage-responsive signal generating means between said primary winding and said gating terminal for applying a signal to said gating terminal when the voltage across said primary winding exceeds a predetermined voltage. 
     
     
       3. The control circuit in claim 1 wherien said transformer includes energy storage means and wherein said primary winding transfers energy to said energy storage means when said control circuit is in said first state and wherein said energy storage means transfers energy to said secondary winding when said control circuit is in said second state unless said protection means is applying said signal to said gating terminal. 
     
     
       4. The control circuit in claim 1 wherein said control signal generating means includes energy storage means and means responsive to the voltage across said primary winding for defining oscillation means for alternatingly applying a signal to said gating terminal and ceasing to apply a signal to said gating terminal. 
     
     
       5. In a control circuit for supplying power to a gas discharge lamp from a power source, said lamp having a gas filled chamber at least one pair of discharge electrodes in said gas filled chamber; said control circuit having an output device with output terminals for connecting with said at least one pair of discharge electrodes, a first input terminal for connection with source of power and a second input terminal for connection with a gated switching device;   said control circuit further having control signal generating means for producing a control signal and providing said control signal to a gating terminal of said switching device to intermittently gate said switching device and thereby cause said output device to deliver power to said lamp, said output device being capable of delivering high voltage power to said lamp to initiate current conductance between said pair of discharge electrodes when said switching device is not being gated, wherein the improvement comprises: voltage responsive conducting means between said gating terminal and one of said input terminals for applying a control signal to said gating terminal in response to an increase in voltage across said input terminals and thereby limiting the voltage developed by said output device;     said voltage responsive conducting means includes selective conducting means for conducting current when said voltage across said input terminals is above a predetermined level;   said voltage responsive conducting means further includes an impedance device between said control signal generating means and said gating terminal to reduce the tendency of current conducted by said selective conducting means from being diverted away from said gating terminal.   
     
     
       6. The improved control circuit in claim 5 wherein said selective conducting means is a zener diode. 
     
     
       7. A control circuit for supplying power to a gas discharge lamp from a power source, said lamp having a gas filled chamber and at least one pair of discharge electrodes in said gas filled chamber, said control circuit comprising: a transformer including a primary winding and at least one secondary winding;   gated switch means including a gating terminal and a pair of switched terminals, at least one of said switched terminals connected with said transformer for selectively applying electrical energy to said primary winding in response to a control signal being supplied to said gating terminal;   control signal generating means for generating a control signal, said control signal generating means including feedback means responsive to electrical energy being supplied to said primary winding for affecting the level of said control signal;   lamp current generating means for generating a current through said gas filled chamber, said lamp current generating means including said secondary winding and means for connecting said secondary winding to said discharge electrodes;   energy storage means operatively associated with said transformer for storing electrical energy such that said control circuit will oscillate between a first state in which said control signal generating means supplies a control signal to said gating terminal causing said switching means to apply electrical energy to said transformer primary winding and said energy storage means, and a second state in which said feedback means responsive to electrical energy being applied to said transformer primary winding to cause said control signal generating means to cease supplying said control signal to said gating terminal such that said switching means ceases to apply electrical energy to said transformer primary winding and said energy storage means releases stored electrical energy to said secondary winding; and   voltage responsive conducting means for applying a signal to said gating terminal in response to an increase in voltage across said primary winding and thereby limiting the voltage across said transformer windings when said control circuit is in said second state;   said voltage responsive conducting means includes selective conducting means for conducting current when said voltage across said transformer winding is above a predetemrined level;   said voltage responsive conducting means further includes an impedance device between said control signal generating means and said gating terminal to reduce the tendency of current conducted by said selective means from being diverted to said control signal generating means when said control circuit is in said second state.   
     
     
       8. The control circuit in claim 7 wherein said selective conducting means is a zener diode.